I did contact tascam and all they did was direct me to their list of acceptable SD cards.
That's a fairly predictable response.
And completely understandable IMO, since they've made it known that cards other than those recommended may prove unreliable(!)
You must work for Tascam! It's not understandable response
AT ALL. First off, if there are severe limitations to the media can be reliably used in the DR70D, that should have been flushed out at the testing stage. It's not quite, but I'd say it's pretty close to a design flaw if only a tiny percentage of the worlds SD card media is able to work in your device.
Second, in their marketing information on their site, it says...'Tracks on the DR-70D are captured to SD card, SDHC or SDXC media – up to 128GB cards are supported.' The first line in their specification sheet says 'SD card(64MB to 2GB), SDHC card(4GB to 32GB), SDXC card(48GB to 128GB)'
With the list of approved media shown, neither of the above statements is true.